1. Field of the Invention
The present invention relates to an apparatus and a method for producing reduced metal in which an agglomerate incorporated with carbonaceous material (hereinafter merely referred to as agglomerate) composed of an iron oxide or nonferrous metal oxide component and a carbonaceous reducing component is fed into a moving hearth reducing furnace to form reduced iron or metal by thermal reduction.
2. Description of the Related Art
A regenerative burner has two gas supply and exhaust portions. One gas supply and exhaust portion is used as a combustion site to burn fuel in the presence of combustion air, while the other portion is used as an exhaust site which inhales hot gases, e.g., atmospheric gas heated by the burner and combustion gas and exhausts them to the exterior. Each air supply and exhaust portion is provided with a regenerator. Heat of the hot gas inhaled in the exhaust site is accumulated in the regenerator and is used to preheat the fuel and the combustion air which are supplied to the burner at the combustion site. The combustion site and the exhaust site are mutually switched to enhance the thermal efficiency by the use of high-temperature exhaust gas. Thus, regenerative burners have been conventionally used for drying and perheating industrial heating furnaces, such as a metal furnace and a heat treating furnace, and radle refractories.
When hot gas in the furnace contains large amounts of dust components and volatile components, the regenerator is concerned about rapid deterioration and contamination by the volatile components, precluding the use of the regenerative burner.
When the furnace is filled with a reducing atmosphere of combustible gas, the combustible gas inhaled in the exhaust site of the regenerative burner poisons the regenerator. Moreover, combustible gas exhausted from the regenerative burner causes environmental contamination.
A collector is provided between the furnace and the regenerator to collect iron oxide as a dust component. Moreover, some regenerators use materials having high corrosion resistance, such as ceramic. In an alternative method, the interiors of the pipes at the exhaust site and the regenerative burner are replaced with inert gas before the exhaust site is switched to the combustion site in order to prevent combustion of combustible gas.
These technologies, however, additional devices, e.g., the collector and a unit for replacing the gas. As a result, the structure of the regenerative burner is complicated, and the regenerative burner requires a large installation space, resulting in increased initial facility costs. Moreover, switching of the regenerative burner from the exhaust site to the combustion site inevitably requires dust removal and inert gas replacement, requiring switching times.
The use of the material having high corrosion resistance such as ceramic causes increased operational costs, since the expensive regenerator must be frequently replaced to new one due to contamination by the volatile components and dust components. Moreover, scrapping of the used regenerator may cause environmental contamination.
In particular, in a plant in which an agglomerate composed of an iron oxide component and a carbonaceous reducing component is fed into a moving hearth reducing furnace to form reduced iron by heating, iron oxide in the raw material is pulverized and is present as dust in the furnace. Moreover, the raw material may contain large amounts of volatile components in some cases. In the reduction process of reduced iron, the furnace is filled with a reducing atmosphere, which is combustible gas formed from the carbonaceous reducing component or combustible gas blown into the furnace, such as natural gas. Thus, large amounts of volatile components are evaporated in the initial stage of the heating for reduction. Moreover, the plant must be maintained at an adequate reducing atmosphere in order to prevent reoxidation of the reduced iron and to maintain a high metallization rate. Accordingly, the use of the regenerative burner is difficult.
Accordingly, it is an object of the present invention to provide an apparatus for producing reduced metal using a regenerative burner.
According to an aspect of the present invention, an apparatus for producing a reduced metal includes a moving hearth reducing furnace for heating a raw material comprising a metal oxide component and a carbonaceous reducing component to form the reduced metal, a feeding section for feeding the raw material into the moving hearth reducing furnace, a metal discharge section for discharging the reduced metal from the moving hearth reducing furnace, a gas discharge section for discharging waste gas from the furnace, the gas discharge section being disposed in a reducing process between the moving hearth reducing furnace and the metal discharge section, and a regenerative burner as a heat source for the moving hearth reducing furnace.
Preferably, the regenerative burner is disposed in the first half stage of the reducing process or a region between the feeding section and the gas discharge section of the moving hearth reducing furnace.
Preferably, the regenerative burner is disposed in a region in which the surface temperature of the raw material is 1,250xc2x0 C. or less, and the gas discharge section is disposed downstream of this region.
Since the regenerative burner is disposed in the first half stage of the reducing process in which volatile components are not significantly volatilized, s regenerator is not deteriorated, and no dust collector is required. Thus, the regenerative burner can be disposed in a small space without increased initial facility costs.
Preferably, the regenerative burner comprises a first regenerative burner for burning a fuel with an oxidizing gas and a second burner for burning a combustible gas in the furnace with an oxidizing gas, the first regenerative burner and the second regenerative burner are disposed in the first half stage of the reducing process, and the second regenerative burner is disposed below the first regenerative burner. Preferably, the regenerative burner burns a combustible gas in the moving hearth reducing furnace with an oxidizing gas, a burner (unregenerative burner) for burning a fuel with an oxidizing gas is disposed in the first half stage of the reducing process, and the regenerative burner is disposed below the burner. In such a configuration, the reducing gas (combustible gas) generated from the interior of the raw material can be effectively burned in the vicinity of the raw material. Thus, the heat transmission effect into the raw material is improved, resulting in promotion of reducing reaction in the raw material.
The raw material may be an agglomerate comprising an iron oxide component and a carbonaceous reducing component. In such a case, the apparatus produces reduced iron. Alternatively, the raw material may be an agglomerate comprising a nonferrous metal oxide component and a carbonaceous reducing component. In such a case, the apparatus produces a reduced nonferrous metal.
The regenerative burner may contain a regenerator comprising one of reduced iron and iron ore agglomerate. These materials are inexpensive, and can be used as a raw material for the apparatus of the present invention after the raw material is contaminated with volatile components and dust. As a result, the waste regenerator can be disposed without increased operational costs and environmental pollution.
Preferably, the regenerative burner is disposed horizontally or slightly upwardly with respect to the hearth of the moving hearth reducing furnace, at the upper portion of the moving hearth reducing furnace in the second half stage of the reducing process or a region between the gas discharge section and the metal discharge section. Preferably, a combustion gas in the regenerative burner in the second half stage is an oxidizing atmosphere, and the raw material is surrounded by a reducing atmosphere. Since the regenerative burner and the vicinity of the agglomerate are maintained at the appropriate atmospheres, substitution using an inert gas is not necessary. Thus, the regenerative burner can be disposed in a small space and can be rapidly switched from the exhaust site to the combustion site. Since the regenerative burner is disposed horizontally or slightly upwardly with respect to the hearth of the moving hearth reducing furnace in the upper portion of the moving hearth reducing furnace, the oxidizing gas does not flow directly toward the surface of the raw material. Thus, the reduced metal is not oxidized by the oxidizing gas, resulting in a high metallization rate.
According to another aspect of the present invention, a method for producing a reduced metal by heating an raw material comprising a metal oxide component and a carbonaceous reducing component, comprises the steps of feeding the raw material into the moving hearth reducing furnace, and heating the raw material by a regenerative burner disposed at the upper portion of the moving hearth reducing furnace while discharging waste gas from the furnace in the first half stage of a reducing process between feeding of the raw material and discharging of reduced iron.
Preferably, the raw material is heated by a regenerative burner which is disposed horizontally or slightly upwardly with respect to the hearth of the moving hearth reducing furnace at a upper portion of the moving hearth reducing furnace in the second half stage of the reducing process, and a combustion gas of the regenerative burner is maintained at an oxidizing atmosphere so that the vicinity of the regenerative burner is maintained at an oxidizing atmosphere and the vicinity of the raw material is maintained at a reducing atmosphere.
Alternatively, the raw material may be heated by a regenerative burner which is disposed in a region in which the surface temperature of the raw material is 1,250xc2x0 C. or less in the first half stage of the reducing process, and the waste gas in the furnace may be discharged at a position downstream of the region in which the surface temperature of the raw material is 1,250xc2x0 C. or less.
In the above method, the regenerative burner is disposed in the first half stage of the reducing process in which volatile components are not significantly volatilized. Thus, the regenerative burner is not deteriorated by the volatile components and a dust collector is unnecessary. The regenerative burner can be disposed in a small space without increased initial facility costs. Since the regenerative burner and the vicinity of the raw material are maintained at the appropriate atmospheres, substitution using an inert gas is not necessary. Thus, the regenerative burner can be disposed in a small space and can be rapidly switched from the exhaust site to the combustion site. Since the regenerative burner is disposed horizontally or slightly upwardly with respect to the hearth of the moving hearth reducing furnace in the upper portion of the moving hearth reducing furnace, the oxidizing gas does not flow directly toward the surface of the raw material. Thus, the reduced metal is not oxidized by the oxidizing gas, resulting in a high metallization rate.
Preferably, a first regenerative burner for burning a fuel with an oxidizing gas and a second regenerative burner for burning a combustible gas in the moving hearth reducing furnace with an oxidizing gas are disposed in the first half stage of the reducing process instead of the regenerative burner, and the second regenerative burner is disposed below the first regenerative burner. Preferably, the regenerative burner burns a combustible gas in the moving hearth reducing furnace with an oxidizing gas, a burner (unregenerative burner) for burning a fuel with an oxidizing gas is disposed in the first half stage of the reducing process, and the regenerative burner is disposed below the burner. In such a configuration, the reducing gas (combustible gas) generated from the interior of the raw material can be effectively burned in the vicinity of the raw material. Thus, the heat transmission effect into the raw material is improved, resulting in promotion of reducing reaction.
Preferably, the regenerative burner contains a regenerator comprising one of reduced iron and iron ore agglomerate. These materials are inexpensive, and can be used as a raw material for the apparatus of the present invention after the raw material is contaminated with volatile components and dust. As a result, the waste regenerator can be disposed without increased operational costs and environmental pollution. The metal oxide component of the agglomerate may be an iron oxide component for producing reduced iron. Alternatively, a part or the entity of the metal oxide component may be a nonferrous metal oxide for producing a reduced nonferrous metal.